Luminaires with automated and remotely controllable functionality are well known in the entertainment and architectural lighting markets. Such products are commonly used in theatres, television studios, concerts, theme parks, night clubs and other venues. A typical product will typically provide control over the pan and tilt functions of the luminaire allowing the operator to control the direction the luminaire is pointing and thus the position of the light beam on the stage or in the studio. Typically this position control is done via control of the luminaire's position in two orthogonal rotational axes usually referred to as pan and tilt. Many products provide control over other parameters such as the intensity, color, focus, beam size, beam shape and beam pattern. The beam pattern is often provided by a stencil or slide called a gobo which may be a steel, aluminum or etched glass pattern. The products manufactured by Robe Show Lighting such as the ColorSpot 700E are typical of the art.
FIG. 1 illustrates a multiparameter automated luminaire system 10. These systems commonly include a plurality of multiparameter automated luminaires 12 which typically each contain on-board a light source (not shown), light modulation devices, electric motors coupled to mechanical drives systems and control electronics (not shown). In addition to being connected to mains power either directly or through a power distribution system (not shown), each luminaire is connected is series or in parallel to data link 14 to one or more control desks 15. The luminaire system 10 is typically controlled by an operator through the control desk 15.
FIG. 2 illustrates a prior art automated luminaire 12. A lamp 21 contains a light source 22 which emits light. The light is reflected and controlled by reflector 20 through an aperture or imaging gate 24. The resultant light beam may be further constrained, shaped, colored and filtered by optical devices 26 which may include dichroic color filters, goboes, rotating goboes, irises, framing shutters, effects glass and other optical devices well known in the art. The final output beam may be transmitted through output lenses 28 and 29 which may form a zoom lens system. Lenses 28 and 29 may individually and separately be constrained to move along the optical axis on slide rails 30 and 32 so as to change the separation of lenses 28 and 29 and the relative position of the lenses to aperture 24 and optical device(s 26. The movement of the lenses may change the effective focal length of the combination and therefore the image focus and image magnification. By adjusting the positions of the lenses the user can select a desired image size and then control the sharpness or focus of that image. The friction or dampening on the movement of lenses 28 and 29 and their interaction with slide rails 30 and 32 is critical to the smooth and accurate operation of the luminaire 12. If the friction is too high then the lenses 28 and 29 may jam or stick on the rail(s) 30 or 32 and movement may be jerky. Additionally excess friction will cause hysteresis problems where a lens 28, 29 will be positioned differently when moving to a preset position in one direction 27 or 31 than when it moves to that same position from the opposite direction 31 or 27 respectively. Such jerky movement and hysteresis will be manifested as poor image quality in the projected beam or noticeable and distracting jumps in the focus and size of the projected image/beam. It is also important that the friction is not too low as that may cause overshoot or wobbling of the lenses 28, 29 as they move. As with many mechanical systems a critical amount of friction or dampening is key to smooth, controlled movement.
FIG. 3 illustrates a prior art mechanism used to control the movement of a lens assembly 100 along the optical axis of an automated luminaire. Lens 102 is rigidly attached to a lens carrier 104. Lens carrier 104 rides on a rail 112 such that lens carrier 104 may slide along cylindrical rail 112 and the lens 102 may be positioned as desired along the optical axis through connection 114 with belt 116. Belt 114 is moved by the rotation of driven pulley 108 and runs on idler 110. In the prior art embodiment illustrated there is a transverse circular hole (not shown in FIG. 3) through lens carrier 120 of as diameter slightly larger than that of the rail 112 so that the carrier moves freely on the rail with the hole acting as a friction beating. It is important that movement is constrained to the optical axis only as any movement transverse to the optical axis will degrade the resultant image. Thus lens carrier 120 is typically long along the optical axis so as to minimize any possible rotation about axes that are orthogonal to the optical axis of lens carrier 120 on slide 112 and ensure that the lens is maintained perpendicular to the optical axis. A disadvantage of this system is that the long contact length between the lens carrier 120 and slide 112 produces excess friction between the two and the movement of the carrier along the slide may be stiff and jerky and also exhibit excess hysteresis. The use of lubricants is problematic as an oily or greasy surface will attract dust and other contaminants which may jam the movement. A further problem is that any deviation in the straightness of rail 112 may cause a jamming of the movement of carrier 120.
FIG. 4 illustrates a further prior art arrangement which seeks to alleviate the friction and sticking problems exhibited by the system shown in FIG. 3. In this case the single long transverse hole in carrier 120 riding on rail 112 is replaced by two shorter segments with transverse holes 122. This arrangement is an improvement over the system shown in FIG. 3 in that it reduces overall friction however it fails to provide repeatable control over that friction. Further it is still prone to the problems involved with lubricants of the carrier and rail.
In prior art automated luminaire slide systems the manufacturers have been forced by operating conditions to provide additional mechanical means to provide a controlled amount of friction or dampening to the movement of the carrier on the rail in order to minimize hysteresis. Typically this takes the form of an adjustable spring loaded plunger (not shown) providing force onto the rail or a friction collar clamping on to the rail with an adjustable amount of force. Both these systems are prone to poor adjustment and drift in adjustment as the fixture ages and is maintained.
There is a need for an improved lens slide system for automated luminaire which provides controllable and repeatable friction or dampening in the movement of the lens.